1. Field of Invention
The invention relates to a cover apparatus and, in particular, to a cover apparatus for wireless local area network (WLAN) cards.
2. Related Art
The electronic information industry has prospered in recent years. The use of many electronic information products also become popular. With the trend of compactness, the unnecessary voltage or current among internal systems of the products generates enormous broadband noises, which seriously affect the functions of the device. This phenomenon is generally referred as electromagnetic interference (EMI). The EMI problem inside the computer is very complicated. The interference sources include the central processing unit (CPU), motors, inverters, relays, switches, transistors, amplifiers, power supplies or other alternate circuits.
Generally speaking, to solve the EMI problem in electronic information products such as the wireless local area network (WLAN) cards, a conventional way is to use an electromagnetic (EM) shielding material to absorb or shield the EM waves. The shielding of electric field is done by disposing an electric field shielding material between two regions. The separate charges in the electric field shielding material produces a shielding effect, preventing the electric field in one region from propagating to the other. Under a high-frequency electric field, one may use materials with larger permittivity, such as metals, to make a plate cover to enclose electronic elements to be protected.
In the WLAN standards IEEE 802.11, the IEEE 802.11a transmission speed can reach as high as 54 Mbps so that it can have wider applications. IEEE 802.11a can effectively reduce multiple path attenuation and select the 5.4 GHz bandwidth with less interference. These advantages are superior to the currently used 802.11b standards (which uses a bandwidth of 2.4 GHz and has a transmission speed of 11 Mbps). Along with the advance in production techniques and the demands for larger bandwidths and higher speeds, IEEE 802.11a is seen as the high-speed WLAN standards in the next generation.
However, since the IEEE 802.11a transmissions speed and bandwidth are higher than those of IEEE 802.11b, the broadband chip for the IEEE 802.11a standards has a higher power consumption. Poor heat dissipation often affects the operation of the broadband chip. Moreover, such high-frequency electronic devices need a cover apparatus to prevent the EMI problem. Currently, conventional metal plate cover apparatuses can only shield the EM field and cannot simultaneously provide good heat dissipation.
An objective of the invention is to provide a cover apparatus for plug-in interface cards to simultaneously provide good heat dissipation and prevent EMI.
Pursuant to the above objective, the disclosed cover apparatus contains a plate, which secures on a circuit board of a plug-in interface card. The plate has at least one concave corresponding to a chip. The concave directly or indirectly contacts the chip to dissipate heat. The cover apparatus also comprises a fastener to secure the plate on the circuit board. By the concave and the fastener, the plate is able to not only shield electromagnetic interference (EMI) but also dissipate heat from the chip.
According to a preferred embodiment of the invention, the fastener secures the plate on the circuit board using nuts and bolts. A clip device and sidewalls are further employed to enhance the fixing of the plate on the circuit board, providing better EMI shielding. The material of the plate, the fastener, the clip device, and sidewalls is a metal or conductive plastic. In addition, a thermal conductive material can be disposed between the concave and the chip-contacted surface, enhancing the thermal conductivity in between.
In addition to EM shielding, the disclosed cover apparatus further utilizes the concave and the fastener to achieve heat dissipation. The invention uses several devices to secure the plate onto the WLAN card, which do not only prevent bad EM shielding and heat dissipation due to ill-assembly but also avoid the exposure of electronic components to protect the WLAN card.